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Supercontinent
In geology, a supercontinent is a land mass comprising more than one continental core, or craton. The assembly of cratons and accreted terranes that form EurasiaAnd to a lesser extent, the Americas, if taken as a whole qualifies as a supercontinent today. History Most commonly, paleogeographers employ the term supercontinent to refer to a single landmass consisting of all the modern continents. The earliest known supercontinent was Vaalbara. It formed from proto-continents and was a supercontinent by 3.1 billion years ago (3.1 Ga). Vaalbara broke up ~2.8 Ga. The supercontinent Kenorland was formed ~2.7 Ga and then broke sometime after 2.5 Ga into the proto-continent cratons called Laurentia, Baltica, Australia, and Kalahari. The supercontinent Columbia, formed and broke up during a period of 1.8 to 1.5 billion years (1.8-1.5 Ga) ago. The supercontinent, Rodinia, broke up roughly 750 million years ago. One of the fragments included large parts of the continents now located in the southern hemisphere. Plate tectonics brought the fragments of Rodinia back together in a different configuration during the late Paleozoic era, forming the best-known supercontinent, Pangaea. Pangaea subsequently broke up into the northern and southern supercontinents, Laurasia and Gondwana. Modern studies have suggested that supercontinents form in cycles, coming together and breaking apart again, through plate tectonics, very roughly about every 250 million years. Geology Supercontinents block the flow of heat from the Earth's interior, and thus cause the asthenosphere to overheat. Eventually, the lithosphere will begin to dome upward and crack, magma will then rise, and the fragments will be pushed apart. It is currently a matter of some debate as to how the supercontinents reform, whether or not plate tectonics makes them re-join after travelling around the planet, or if they move apart and then back together again. In other areas of study such as history and geography, land masses connected with an isthmus are also considered supercontinents or just continents, such as the Americas. Some historians call the combined land mass of Africa and Eurasia the supercontinent Africa-Eurasia. Incomplete list of minor past supercontinents These are supercontinents that comprised only a fraction of the land on Earth. * Euramerica * Gondwana * Laurasia * Nena Incomplete list of supercontinents In reverse-chronological order (stratolithic order) comprising nearly all land at the time. *Pangaea Ultima or Amasia (~250 – ~400 million years from now (future supercontinent)) *Austro-Antarctica-Eurafrasia (~130 million years from now (future supercontinent)) *Austro-Eurafrasia (~60 million years from now (future supercontinent)) *Eurafrasia (~30 million years from now (future supercontinent)) *Americas (~ 15 mya present-day supercontinent) *Eurasia (~ 60 mya present-day supercontinent) *Gondwana (~600 – ~30 million years ago) *Laurasia (~ 300 – ~60 million years ago) *Pangaea (~300 – ~180 million years ago) *Euramerica (~ – ~300 million years ago) *Pannotia (~600 – ~540 million years ago) *Rodinia (~1.1 Ga – ~750 million years ago) *Columbia, also called Nuna, (~1.8–1.5 Ga ago) *Kenorland (~2.7 Ga. Neoarchean sanukitoid cratons and new continental crust formed Kenorland. Protracted tectonic magna plume rifting occurred 2.48 to 2.45 Ga and this contributed to the Paleoproterozoic glacial events in 2.45 to 2.22 Ga. Final breakup occurred ~2.1 Ga.) *Ur (~3 Ga ago, though probably not a supercontinent; but still however, the earliest known continent. Ur, however, was probably the largest, perhaps even the only continent three billion years ago, so one can argue that Ur was a supercontinent for its time, even if it was smaller than Australia is today). Still an older rock formation now located in Greenland dates back from hadean *Komatii Formation (3.475 Ga) *Vaalbara (~3.6 Ga ago. Evidence is the Yilgarn Craton, Western Australia and the world-wide Archean greenstone belts that were subsequently spread out across Gondwana and Laurasia) *Yilgarn (Zircon crystals from the Jack Hills of the Narryer Gneiss Terrane, Yilgarn craton, Western Australia and also 300 km. south point to a continental crust formation between 4.4-4.3 Ga. Evidence is the high Oxygen-18 values of 8.5 and micro-inclusions of SiO2 in these zircon crystals consistent with growth from a granitic source supracrustal material, low-temperature interactions and a liquid ocean.) Notes See also * Superoceans * Plate tectonics * List of supercontinents * Supercontinent cycle External links *Palaeos.com: General earth history *The Paleomap Project — Christopher R. Scotese *Graphical overview of the Supercontinents on WikiTimeScale.org * Category:Historical geology Category:Supercontinents